The present invention relates to a process for producing ultra-high purity isopropyl alcohol. More particularly, the present invention relates to a process for producing ultra-high purity isopropyl alcohol that has less than 100 parts per trillion of metal impurities and less than 100 parts per million water.
Semiconductor manufacturing operations require that wafer surfaces be as clean as possible. At times this is difficult, especially when the wafer or chip is rinsed with an aqueous solution and subsequently dried. The process of drying often leads to the formation of spots, leaving unwanted residue on the surface. This can be a nuisance that leads to defects in the manufacturing process.
One solution to this residue problem is to immediately follow the aqueous rinse with a rinsing solution containing isopropyl alcohol. The isopropyl alcohol quickly evaporates, leaving no residue behind.
In order for this method to be effective, the isopropyl alcohol must be extremely pure. This new requirement has created a need to develop processes that purify isopropyl alcohol to unusually high purity levels, typically where contaminants and water are measured in parts per million and/or lower.
Several patents describe processes used to produce a high purity isopropyl alcohol product. However, none of these patents disclose the processes described and claimed by the present invention:
U.S. Pat. No. 5,868,906 issued to Adams et al. on Feb. 9, 1999 teaches a method for dehydrating and purifying impure isopropyl alcohol by removing substantially all the water and any organic impurities with boiling points less than isopropyl alcohol from an isopropyl alcohol solution containing less than 2000 parts per million water in a first distillation column. The overhead product contains organic substances with boiling points less than isopropyl alcohol and a binary isopropyl alcohol/water azeotrope. The overhead product from the first distillation column feeds a second distillation column, where a low boiling overhead product is taken and filtered to a desired specification.
U.S. Pat. No. 2,604,440 issued to Brooks on Jul. 22, 1952 discloses a process where isopropyl alcohol is purified by removing water from an isopropyl alcohol-water binary azeotrope in the presence of sulfuric acid.
U.S. Pat. No. 4,399,000 issued to Tedder on Aug. 16, 1983, teaches a process for producing alcohol substantially free of water. The process comprises the steps of extracting an aqueous alcohol solution with an organic solvent system containing an extractant for the alcohol, thereby forming an organic solvent-alcohol phase and an aqueous phase, and vacuum distilling the organic solvent-alcohol phase thereby obtaining the product alcohol substantially free of water.
U.S. Pat. No. 5,585,527 issued to Marker on Dec. 17, 1996 and U.S. Pat. No. 5,571,387 issued to Marker et al. on Nov. 5, 1996, disclose processes that involve distillation by fractionation and membrane separation by vapor permeation in a single vessel. The distillation zone can be positioned upstream or downstream of the membrane separation zone. The process can be used to separate alcohol, e.g. isopropyl alcohol, and water.
U.S. Pat. No. 5,897,750 issued to Berg on Apr. 27, 1999 describes a method that uses extractive distillation for separating acetone, isopropyl alcohol, and water.
U.S. Pat. No. 5,494,556 issued to Mita et al. discloses a method for separating a liquid mixture, such as isopropyl alcohol and water. In the method, the liquid mixture is heated then supplied to a pervaporation membrane module to separate a permeable component of the liquid, a portion of non-permeated liquid is circulated through a circulation pipe into a liquid mixture feeding pipe before a heater, and the remaining portion of the non-permeated liquid is extracted to the outside of the system, and wherein the temperature of the liquid mixture feeding pipe in which the non-permeated liquid has been mixed with the liquid mixture or in the circulation pipe for the non-permeated liquid, is measured, and when the measured temperature is out of a predetermined range, new supply of the liquid mixture and/or extraction of the non-permeated liquid is stopped.
The methods taught in the prior art, do not necessarily meet the requirements of today""s customers, such as the semiconductor industry. As such, a process for preparing ultra-high purity isopropyl alcohol is needed to meet the new demands of customers.
The present invention also provides many additional advantages which shall become apparent as described below.
The present invention is directed to a process for producing high purity isopropyl alcohol. The process comprises the steps of: (a) feeding a feed stream comprising at least about 99.9 wt. % isopropyl alcohol into a separation column; (b) separating the isopropyl alcohol into an overhead stream which is taken overhead from the separation column and a bottoms stream taken as bottoms from the separation column; and (c) removing the high purity isopropyl alcohol at a point: (i) below where the feed stream enters the separation column but above the bottoms stream, or (ii) above where the feed stream enters the separation column but below the overhead stream, wherein the high purity isopropyl alcohol has a metals content of less than about one part per billion (ppb) and a water content of less than about 100 parts per million (ppm). Optionally, the process includes the further step of passing the high purity isopropyl alcohol through an ion exchange resin after removing the high purity isopropyl alcohol from the separation column, thereby forming an ultra-high purity isopropyl alcohol that contains less than 100 parts per trillion (ppt) of any metal impurity.
High purity isopropyl alcohol may also be produced by a process comprising the steps of: (a) feeding a feed stream comprising at least about 99.9 wt. % isopropyl alcohol into a separation column; (b) separating the isopropyl alcohol into an overhead stream which is taken overhead from the separation column and a bottoms stream taken as bottoms from the separation column, wherein the overhead stream comprises the high purity isopropyl alcohol having a metals content of less than about 1 ppb and a water content of less than about 100 ppm. The high purity isopropyl alcohol may further be processed through an ion exchange resin after collecting the high purity isopropyl alcohol from the overhead stream, thereby forming an ultra-high purity isopropyl alcohol that contains less than 100 ppt metal impurities.